Hubble orbit?

The subject of STS-125 and the Hubble's orbit came up on another group.
I misremembered it being in an equatorial orbit when of course (duh) it
was launched into the same inclination as the 28.5-deg latitude of the
Cape. But this got me to wondering why they didn't put Hubble in an
equatorial orbit, considering the possible benefits of less complicated
celestial tracking and orbital issues such as precession. Was the
28.5-deg orbit chosen mainly because the Shuttle doesn't have the fuel
capacity to do an equatorial dog-leg maneuver, even with the assist of
the OMS during the launch phase, with a payload as massive as Hubble?
Could the Shuttle have used the OMS engines to make an orbital plane
change from a temporary 28.5-deg orbit into an equatorial one before
releasing the Hubble? Perhaps the answer is they would have if they
could have.

"flyguy" wrote in message
...
The subject of STS-125 and the Hubble's orbit came up on another group. I
misremembered it being in an equatorial orbit when of course (duh) it was
launched into the same inclination as the 28.5-deg latitude of the Cape.
But this got me to wondering why they didn't put Hubble in an equatorial
orbit, considering the possible benefits of less complicated celestial
tracking and orbital issues such as precession. Was the 28.5-deg orbit
chosen mainly because the Shuttle doesn't have the fuel capacity to do an
equatorial dog-leg maneuver, even with the assist of the OMS during the
launch phase, with a payload as massive as Hubble?

That is it.

Could the Shuttle have used the OMS engines to make an orbital plane
change from a temporary 28.5-deg orbit into an equatorial one before
releasing the Hubble? Perhaps the answer is they would have if they could
have.



--
Greg Moore
Ask me about lily, an RPI based CMC.

flyguy wrote:
The subject of STS-125 and the Hubble's orbit came up on another group.
I misremembered it being in an equatorial orbit when of course (duh) it
was launched into the same inclination as the 28.5-deg latitude of the
Cape. But this got me to wondering why they didn't put Hubble in an
equatorial orbit, considering the possible benefits of less complicated
celestial tracking and orbital issues such as precession.

It's expensive and probably beyond the capability, but the perceived
advantages are minimal if any. It's not significantly more complex to
handle 28.5 degrees than it is fractions of a degree. It's not like you
could just assume it was zero, you would still have to use the actual
orbit. Might as well be 28 as ~0.

Brett

Was there not also the problem of bringing it down somewhere remote to be
considered?
Brian

--
Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
Email:
__________________________________________________ __________________________________________________ __________


"Brett Buck" wrote in message
...
flyguy wrote:
The subject of STS-125 and the Hubble's orbit came up on another group. I
misremembered it being in an equatorial orbit when of course (duh) it was
launched into the same inclination as the 28.5-deg latitude of the Cape.
But this got me to wondering why they didn't put Hubble in an equatorial
orbit, considering the possible benefits of less complicated celestial
tracking and orbital issues such as precession.

It's expensive and probably beyond the capability, but the perceived
advantages are minimal if any. It's not significantly more complex to
handle 28.5 degrees than it is fractions of a degree. It's not like you
could just assume it was zero, you would still have to use the actual
orbit. Might as well be 28 as ~0.

Brett

On Mar 22, 7:54*pm, flyguy wrote:
The subject of STS-125 and the Hubble's orbit came up on another group.
I misremembered it being in an equatorial orbit when of course (duh) it
was launched into the same inclination as the 28.5-deg latitude of the
Cape. But this got me to wondering why they didn't put Hubble in an
equatorial orbit, considering the possible benefits of less complicated
celestial tracking and orbital issues such as precession. Was the
28.5-deg orbit chosen mainly because the Shuttle doesn't have the fuel
capacity to do an equatorial dog-leg maneuver, even with the assist of
the OMS during the launch phase, with a payload as massive as Hubble?
Could the Shuttle have used the OMS engines to make an orbital plane
change from a temporary 28.5-deg orbit into an equatorial one before
releasing the Hubble? Perhaps the answer is they would have if they
could have.

No vehicle has that capability to do that in LEO. The impulse
requirements are large. GSO spacecraft do it at attitude where the
velocity requirements are much smaller

The OMS assist provides a performance increase by dumping weight, the
engine thrust addition is negligible

wrote:

No vehicle has that capability to do that in LEO. The impulse
requirements are large. GSO spacecraft do it at attitude where the
velocity requirements are much smaller

At what point do they adjust their orbit during launch ?

Do they fly straight east from 28.5 and "turn" once they reach the
descending node at equator ?

Or do they fly south east on launch until they reach equator and then
turn where they accelerate into proper due east ?

Or do they actually reach 28.5 LEO, and only while boosting to geosync
altitude do they adjust the orbit to become equatorial ?

John Doe wrote:
wrote:

At what point do they adjust their orbit during launch ?

Do they fly straight east from 28.5 and "turn" once they reach the
descending node at equator ?

Or do they fly south east on launch until they reach equator and then
turn where they accelerate into proper due east ?

Or do they actually reach 28.5 LEO, and only while boosting to geosync
altitude do they adjust the orbit to become equatorial ?

Not while boosting, after you get there (or higher even). To do a plane
change while keeping the same speed, the velocity change is
approximately:

dV = 2V * sin(theta / 2)

Where V is the initial (and final) orbital speed and theta is the
angular difference between the planes. So doing the change when the
velocity is at a minimum (at the highest altitude) is important.

Combining it with another burn (such as a circularizing burn at apogee)
would use less fuel than both independently, though.

--
Darren

On Mar 23, 1:14*pm, John Doe wrote:
wrote:
No vehicle has that capability to do that in LEO. *The impulse
requirements are large. *GSO spacecraft do it at attitude where the
velocity requirements are much smaller

At what point do they adjust their orbit during launch ?

Do they fly straight east from 28.5 and "turn" once they reach the
descending node at equator ?

Or do they fly south east on launch until they reach equator and then
turn where they accelerate into proper due east ?

Or do they actually reach 28.5 LEO, and only while boosting to geosync
altitude do they adjust the orbit to become equatorial ?

Neither of them

They fly near due east and enter a LEO orbit of around 28.5 (for less
than a quarter of an orbit). When the vehicle crosses the equator,
the upperstage fires to put the spacecraft in a GTO. Upon apogee, the
spacecraft fires its propulsion system to zero out the inclination and
raise the perigee to GSO altitude.

wrote:
Neither of them

They fly near due east and enter a LEO orbit of around 28.5 (for less
than a quarter of an orbit). When the vehicle crosses the equator,
the upperstage fires to put the spacecraft in a GTO. Upon apogee, the
spacecraft fires its propulsion system to zero out the inclination and
raise the perigee to GSO altitude.

Or they do a bi-elliptic.
http://en.wikipedia.org/wiki/Bi-elliptic_transfer

The article only talks about the changes to in-plane circular orbits,
but because a plane change can be done with the second burn at a higher
apogee, there are further savings if one is involved.

WGS-2 will launch this way with a transfer orbit reaching 67000km.

--
Darren

On Mar 25, 6:28*pm, (Darren Dunham) wrote:
wrote:
Neither of them

They fly near due east and enter a LEO orbit of around 28.5 (for less
than a quarter of an orbit). *When the vehicle crosses the equator,
the upperstage fires to put the spacecraft in a GTO. *Upon apogee, the
spacecraft fires its propulsion system to zero out the inclination and
raise the perigee to GSO altitude.

Or they do a bi-elliptic.
http://en.wikipedia.org/wiki/Bi-elliptic_transfer

The article only talks about the changes to in-plane circular orbits,
but because a plane change can be done with the second burn at a higher
apogee, there are further savings if one is involved.

WGS-2 will launch this way with a transfer orbit reaching 67000km.

--
Darren

WGS-2 method is called supersynchronous transfer and isn't really bi-
elliptic since there are many intermediate orbits